212 RESPIRATION. 



son breathing air. The quantity over and above this which 

 a man can draw into the lungs in the deepest inspiration, 

 he names complemented air : its amount is various, as will 

 be presently shown. After ordinary expiration, such as 

 that which expels the Ireathing air, a certain quantity of 

 air remains in the lungs, which may be expelled by a 

 forcible and deeper expiration : this he terms reserve air. 

 But, even after the most violent expiratory effort, the 

 lungs are not completely emptied; a certain quantity 

 always remains in them, over which there is no voluntary 

 control, and which may be called residual air. Its amount 

 depends in great measure on the absolute size of the chest, 

 and has been variously estimated at from forty to two 

 hundred and sixty cubic inches. 



The greatest respiratory capacity of the chest is indicated 

 by the quantity of air which a person can expel from his 

 lungs by a forcible expiration after the deepest inspiration 

 that he can make. Mr. Hutchinson names this the vital 

 capacity: it expresses the power which a person has of 

 breathing in the emergencies of active exercise, violence, 

 and disease ; and in healthy men it varies according to 

 stature, weight, and age. 



It is found by Mr. Hutchinson, from whom most of our 

 information on this subject is derived, that at a temperature 

 of 60 F., 225 cubic inches is the average vital capacity of a 

 healthy person, five feet seven inches in height. For every 

 inch of height above this standard the capacity is increased, 

 on an average, by eight cubic inches ; and for every inch 

 below, it is diminished by the same amount. This relation 

 of capacity to height is quite independent of the absolute 

 capacity of the cavity of the chest ; for the cubic contents 

 of the chest do not always, or even generally, increase with 

 the stature of the body ; and a person of small absolute 

 capacity of chest may have a large capacity of respiration, 

 and vice versd. The capacity of respiration is determined 

 only by the mobility of the walls of the chest ; but why 



